It is the ultimate aim of this study to elucidate the specific role of relaxin as a hormone of pregnancy in humans. Presently we have determined and published the structure of the porcine hormone and are in the process of elucidating the structure of the prohormone as well as that of a relaxin-effective peptide from shark ovaries. Structure function studies are aided by the fact that relaxin is a disulfide homolog of insulin. The in vivo action of relaxin will be investigated by measuring its effect on the macromolecular components of the target organs.